Proposal for automatic instance list maintenance

[syeopite]

Once either #74 or #76 is merged we should be able to automate instance list maintenance through github actions. Here's an idea of how this may work:

1. Query instance API
2. Scans each instance and
   • Validate version date to make sure it is less than thirty days away from iv-org/invidious's latest commit.
   • Validate health to be >= 90%
3. If either check fails it is removed.
4. Create PR with the changes.